This is the Battery Buzzer Low Voltage LiPo Battery Alarm from Hitec.

FEATURES: LED status indicator warns pilot when LiPo flight battery is low Programmable voltage threshold allows advance warning to be set by pilot Protects model from unwanted landings and batteries from over- discharging High pitch warning sound Ideal for all electric aircraft using LiPo batteries

INCLUDES: Battery Buzzer LiPo Battery Alarm, with Instructions

SPECS: Input Voltage: 7.4 - 16.8V Battery Type: 2-4S LiPo Voltage Select: 3.2V/3.3V/3.4V/3.5V ±0.05V Net Weight: 0.39oz (11g) Dimensions: 1.97 x 1.10 x .49" (50 x 28 x 12.4mm)  

BOX DIMENSIONS: 2.25" W. X .63" H. X 3.00" L. BOX WEIGHT: .03 LBS.